Most mobile machines are equipped with some kind of brake system that can be used to slow the machines in response to operator input. Typical brake systems implement various control strategies, which adjust the braking applied to a wheel of a machine when underfoot conditions necessitate the adjustments. Two of these control strategies are known as anti-lock braking system (ABS) and dynamic stability control (DSC).
ABS is a control strategy that tries to reduce wheel slip during braking in order to improve the ability to steer the machine. In some cases, ABS can improve stopping distance or braking ability, but the primary goal is to improve steering control by reducing slip. When ABS is active, it will decrease braking torque on the wheel when it senses the wheel beginning to lose too much rotation (to slip) in relation to the other wheels of the machine or the moving ground below.
DSC detects an actual yaw-rate (turning) of the machine, a desired yaw-rate (steering), and estimated machine slide-slip. When these rates differ due to poor underfoot conditions, DSC attempts to correct for the difference by appropriately applying braking force to one or more of the wheels. Braking forces are applied to individual wheels asymmetrically in order to create torque about the machine's vertical axis and help the machine track the desired yaw-rate, despite side slip.
ABS and DSC can both improve machine control and stability, and the two in combination may or may not be conflicting. ABS must take into account maximum limits of brake forces happening on both sides of the machine, while DSC must manage the difference between brake forces acting on each side of the machine. Sometimes ABS will set upper limits on the braking force to prevent locking of the wheels. Sometimes DSC will determine an optimal braking force that is not within the limits set by ABS.
An exemplary brake system having a vehicle dynamic control system including ABS to stabilize cornering movement of a vehicle is disclosed in U.S. Application No. EP 2208651 issued to Semsey on Jul. 21, 2010 (the '651 application”). Specifically, the '651 application discloses a system that calculates an acceleration vector of a cornering vehicle based on measurements of longitudinal and lateral components of acceleration, while the ABS modifies at least three wheel brake forces. The system determines whether this corner acceleration falls within a forbidden range of acceleration vectors, which causes side slip and instability of the vehicle. If the acceleration falls within the forbidden range, and requires adjustment, the system applies a brake force or slip to the outer front wheel to bring the vehicle acceleration into an acceptable state.
While the system of the '651 patent may provide desired braking for cornering stability during ABS activation, the system does not discuss DSC brake commands. Furthermore, the '651 patent does not discuss how to handle a situation in which DSC brake commands conflict with concurrent ABS commands.
The present disclosure is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.